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Power Line Circuits
Last Updated on: Monday, October 03, 2011 06:07 PM


Circuits Designed by Dave Johnson, P.E. :
  • ISOLATED AC CURRENT MONITOR
    This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding....
  • Miniature 5v Line Powered Isolated Supply
    Often a circuit requires a 5v DC supply to power some logic circuits.  The conventional method is to use an AC wall adapter.  But, many systems, which bring AC power onto a circuit board, need a small AC to DC power supply right on the circuit board.  The circuit below provides such a supply.  It uses a classic series capacitor charge pump which acts as a current limiting device.  A full wave rectifier, a filter capacitor and a zener diode provide an off-the-shelf isolated DC to DC converter with a 24v DC input.  The miniature converter from CUI generates a regulated +5v output, rated at 100ma.  By doubling the size of the capacitor C1 the circuit can be pushed to produce 200ma of output current.  Also, the same front end circuit can be used with other CUI converters.  They sell 3.3v, 12v and 15v supplies as well as the 5v unit shown.
  • UNPLUGGED POWER CORD ALARM
    Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged...
  • Unplugged Appliance Alarm
    I got a call from an administrator at a large prison.  He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens...
Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

220 Volt Live Wire in Wall Scanner -  This little circuit will help you to scan  line of a 220V live wire in  wall.  FET gate is connected to a capacitive metal sensor (which is usually a simple metal plate). When you hold  sensor close to  wall,  LED will indicate  current flow around where it detects  wire. Works on 9VDC.... [Peter Jakab, Electrical Engineer, Engineer of Informatics]
3˝ Digit DVM IC Measures Power Factor -  04/28/94 EDN-Design Ideas....Circuitry in Fig 1 allows  ICL7106/7107] digital-voltmeter IC, IC4, to measure power factor to0.1% resolution and operate from a single 9Vdc supply. An important feature of  circuit is that variations in load current, line voltage,.... [Design Idea by Devadoss John and KRS Sarma, Hindustan Cables Ltd, Hyderabad, India]
Ac Line Powered LED Pilot Light -  This simple circuit can be used to light a LED indicator lamp, powered from the 120vac line.  I have included component values for 240vac lines as well.. [Designed by David A. Johnson]
AN-872: TP3420A Line Interface Circuit Considerations -  National Semiconductor Application Note....[App Note]
Calculating Power Dissipation for Differential Line Drivers -  National Semiconductor Application Note  (app note added 2/06)

Isolated AC Current Monitor -  This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding.  The transformer contains a single turn primary with a low 0.001-ohm resistance.  It can easily handle 30 amps of AC current and provides at least 500vac of isolation.  With the components shown, the output AC voltage is scaled so 1 amp of current produces 100mv of AC voltage.... [Designed by David A. Johnson]
Line Powered 60hz Clock Generator -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit.... [Designed by David A. Johnson]
Line Powered White LED Array  -  There has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed into the light fixtures, these LED lights can produce more light with less electricity and last much longer than other devices.  They can also operate well in cold temperatures.  Some of these new lighting fixture designs use a large number of white LEDs, wired into long series wired string arrays.  The circuit below is designed to provide a regulated DC voltage for these strings.  [Designed by David A. Johnson]
Line Powered Xenon Flash Transmitter -  This line powered xenon flash circuit drives a small camera type flash tube. It has an optical isolator to allow the flash to be safely triggered from some remote device. A flash rate of 2Hz is possible with the circuit. …. [Designed by David A. Johnson]
Miniature 5v Line Powered Isolated Supply -  Often a circuit requires a 5v DC supply to power some logic circuits.  The conventional method is to use an AC wall adapter.  But, many systems, which bring AC power onto a circuit board, need a small AC to DC power supply right on the circuit board.  The circuit below provides such a supply.  It uses a classic series capacitor charge pump which acts as a current limiting device. .... [Designed by David A. Johnson]
Off Line Power Supply Requires Few Parts -  02/17/94 EDN-Design IdeasThis simple non-isolated off-line power supply can provide up to150 mA5V and uses only a handful of components from110-230-Volt AC input voltage. Note that the low voltage output is directly connected to the mains; it cannot be used when the low voltage part can be touched.... [Design Idea by Sam Ochi, IXYS Corp, Santa Clara, CA]
Unplugged Appliance Alarm -  I got a call from an administrator at a large prison.  He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area.  He wanted a battery-powered device, which could be mounted to the outside of the power cord of an appliance.  The device would produce a loud alarm whenever the power plug of the appliance was unplugged from a power outlet.... [Designed by David A. Johnson]
Unplugged Power Cord Alarm  -  Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. The device was designed to snap onto the outside of a power cord, where it senses the AC electric field emitted. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.... [Designed by David A. Johnson]


 
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